Whey heated

The ratio of a-lactose [10039-26-6] and P-lactose in dry milk and whey varies according to the speed and temperature of drying. An aqueous solution at equiHbrium at 25°C contains 35% a- and 63% -lactose. The latter is more soluble and sweeter than DL-lactose and is obtained by heating an 80% DL-lactose [63-42-3] solution above 93.5°C, foUowed by drying on a dmm or roUer dryer. Lactose is used for foods and pharmaceutical products. 

Casein. Milk contains proteins and essential amino acids lacking in many other foods. Casein is the principal protein in the skimmed milk (nonfat) portion of milk (3—4% of the weight). After it is removed from the Hquid portion of milk, whey remains. Whey can be denatured by heat treatment of 85°C for 15 minutes. Various protein fractions are identified as a-, P-, and y-casein, and 5-lactoglobulin and blood—semm albumin, each having specific characteristics for various uses. Table 21 gives the concentration and composition of milk proteins. 

Whey proteins that have been heat precipitated under very high shear have a particle size between 1 and 3 micrometers, and give the impression of fat in some products. These microparticulated whey proteins are being used as fat replacers in frozen desserts and processed cheese substitutes. 

Milk from cows contains 3.2% protein, about 80% of which is casein. Casein is isolated by a precipitation process from milk, involving heating, rinsing to remove whey, and drying to a powder. The yield is about 3 kg/ 100 kg skim milk. Rennet casein is obtained when the casein is precipitated by chymosin enzyme, also known as rennet, and acid casein is produced when precipitation is accomplished by acidification. Acid casein is usually found in the form of sodium caseinate or calcium caseinate, which are water-soluble salts. Caseinates are made by reacting NaOH or CaOH with a slurry of casein curd or powder and then spray drying (Southward, 2010). 

Purely thermal denaturation of proteins requires much longer times collagen in moist heat below 120 °C needs 30 min to denature (Meyer et ah, 2005), wheat glutens must be subjected to 200-215 °C of dry heat for 72 min (Friedman et ah, 1987), and as mentioned above, whey proteins require at least 50 °C and 30 min for texturization without the use of extrusion processing. 

We have created structured networks in whey proteins using mild heat and shear, to create reversible TWPs. By understanding on a molecular basis, the effects of shear, ways of creating new functionality can be developed. This will enable development of extrusion parameters that permit controlled denaturation of whey proteins. 

These assumptions were confirmed by the electrophoresis study of the washed creams. Electrophoresis of purified fat globules is a convenient method to characterize and quantify proteins adsorbed at the oil-water interface [35]. Electrophoretic data indicate that no casein, nor whey proteins, were adsorbed at the surface of raw-milk fat globule. Upon homogenization, caseins adsorbed preferentially at the lipid-water interface. In this case, bound a-lactalbumin accounted for 16% of the total interfacial proteins. Heat treatment also induced the interaction of proteins with the fat globules. The amount of bound proteins (per mg of lipids) for heated raw milk was half that for homogenized milk. 

Milk Proteins. As some milk proteins will gel on heating and others can be modified to make whipping agents it has long been thought that milk proteins could be used as whole or partial substitute for egg proteins. Purified whey proteins were regarded as a suitable raw material as whey is a low value by-product from cheese making. Early... 

The heat treatment leads to whey proteins becoming adsorbed, altering the behavior of the micelle. Dehydration by ethanol, for example, leads to aggregation of the micelles. 

Chemical reactions Polymerization of casein and whey proteins are due to some kind of chemical reactions. The different proteins as found in the supernatant of milk after precipitation at pH 4.6 are collectively called whey proteins. These globular proteins are more water soluble than caseins and are subject to heat dena-turation. Denaturation increases their water-binding capacity. The principal fractions are P-lactoglobulin, a-lactalbumin, bovine serum albumin (BSA), and immunoglobulins (Ig). 

Figure 3.2 Evolution of the microstructure of phase-separated biopolymer emulsion system containing pectin and 0.5 vt% heat-denatured (HD) whey protein isolate (WPI) stabilized oil droplets, (a) Composition 1U 3L (one-to-three mass ratio of upper and lower phases). The large circles are the water droplets (W), while the small circles are the oil droplets (O). This system forms a W2/W1-O/W1 emulsion, where O is oil, Wi is HD-WPI-rich and W2 is pectin-rich, (b) Composition 2U 2L. This system forms an 0/Wi/W2 emulsion, where O is oil, Wi is HD-WPI-rich and W2 is pectin-rich, (c) Composition 3U 1L. This system forms an 0/W]/W2 emulsion, where O is oil, Wi is HD-WPI-rich and W2 is pectin-rich. Reproduced from Kim et al. (2006) with permission.

Kim, H.-J., Decker, E.A., McClements, D.J. (2006). Preparation of multiple emulsions based on thermodynamic incompatibility of heat-denatured whey protein and pectin solutions. Food Hydrocolloids, 20, 586-595. 

We turn now to the other major whey protein, p-lactoglobulin. This is an acidic globular protein (p/= 5.1) with a molar mass of 18.4 kDa and a radius of about 2 nm (Aymard et al., 1999). The protein can form long semi-flexible fibrils when heated in solution at around or above its dena-turation temperature (60-80 °C) at pH = 2 and low ionic strength (Durand et al., 2002 Veerman et al., 2002, 2003a,b). (An example of the... 

Bikker, J.F., Anema, S.G., Li, Y., Hill, J.P. (2000). Rheological properties of acid gels prepared front heated milk fortified with whey protein mixtures containing the A, B and C variants of p-lactoglobulin. International Dairy Journal, 10, 723-732. 

Bryant, M.C., McClements, D.J. (1998). Molecular basis of protein functionality with special consideration of cold-set gels derived from heat-denatured whey. Trends in Food Science and Technology, 9, 143-151. 

Ikeda, S., Morris, V.J. (2002). Fine-stranded and particulate aggregates of heat-denatured whey proteins visualized by atomic force microscopy. Biomacromolecules, 3, 382-389. 

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